Lichen recolonisation in an urban-industrial area of southern Poland as a result of air quality improvement.

Dynamics of epiphytic lichen distribution and diversity in the town of Skawina, one of the major industrial centres of southern Poland, over the last 30 years, was documented in relation to air quality changes. Fieldwork was conducted in 2006-2007. A total of 34 species were recorded at 202 sites, which is similar to the historical data, however, significant qualitative changes occurred. Nitrogen- and dust-tolerant species have expanded and dominate, while some acidophytes, such as Lecanora conizaeoides, are in decline. Lichens have recolonised the former 'lichen desert' in the town centre. Species richness at study sites has increased; and an improvement in the health of lichen thalli was noted. These trends reflect air quality improvement, mainly SO(2) decline in the last few decades and transport-related compounds, mainly NO(x) and dust that have became the main pollutants. Host tree species and diameter diversity also contribute significantly to lichen species diversity in the study area. The recolonisation process seems far from complete and further changes in the lichen distribution and diversity in the study area are expected.